Chaos Theory
by psyraven
Summary: Rayne. Small actions can have big consequences, as Jayne, River and the rest of the Serenity crew are about to find out. Irredeemably fluffy, and hopefully humorous, this was originally posted at Copper for a Kiss in 2006.
1. The Smallest Things

Disclaimer: Not mine. Never will be either. I just play with them for fun, while Joss is otherwise distracted.

A/N: Written in response to crazywriterchic's challenge on Copper for a Kiss that '_One turns the other down for sex'_, way back in 2006 or so. First of a series of interconnected stories called Chaos Theory.

* * * * * * * *

**The Smallest Things**

They finally had the place to themselves. Everyone else had headed out for a little well-deserved shore leave, with Simon and Kaylee practically tripping over themselves at the thought of a proper date. Couldn't understand the fuss himself – two of them had been sexing each other up every which way for a few months now. You'd think they'd quit being soppy already. Mal and Inara had taken Zoe out to a bar in an effort to cheer her up a bit, though how successful that was likely to be he didn't know. Hell, the woman had lost her husband and even if he had been a waste of space most of the time in Jayne's personal opinion, you couldn't expect a person to just get over something like that. That left Jayne guarding the ship, a duty he'd volunteered for, making the captain just a mite suspicious.

"We got a chance to go ashore for the first time in over a month and you ain't itching to get yourself a hooker?" Mal had asked when they had that discussion. "You ain't sickening for nuthin' are ya, Jayne?"

"We're gonna be here for a week, ain't we?" he'd replied, not looking the man right in the eyes. Mal had a way of seeing right through a person and he didn't want him thinking about this too hard. "Can go get sexed up any time. Don't have to be right this minute."

"If you say so," Mal said, not looking entirely convinced. "Anyway, River'll be here to keep an eye on you. I'll tell her if you misbehave she can shoot you. You know, somewhere non-lethal." He grinned and punched Jayne on the shoulder.

"Gee, thanks." Course, there was a time when the captain wouldn't have left him and the girl alone on the same ship for all the gold in the Alliance. But then, there was a time they'd have killed each other soon as looking. Things were a mite different, these days. He'd sort of gotten used to her over time, even started understanding some of her gibberish, which was all manner of scary. Then there'd been Miranda, and the Reaver fire fight at Mr. Universe's place. Let's just say his attitude towards her changed after he saw her standing there with a pair of dripping blades over a pile of Reaver corpses. That was one hell of a woman by anyone's reckoning.

After that, they'd gotten along pretty well, sparring now and then so both of them could keep battle-ready. Course, her brother hated that, which just made it all the more fun. Watching the doc get his knickers in a twist was the best form of entertainment on this ship. Mind you, if he knew all of it, they'd probably get wedged so far up his ass he could yank them out of his mouth. It was almost tempting, except for the bit where the doc tells Mal and Mal shoots him in the balls. Nope. Some things were best kept quiet.

He whistled as he headed towards the galley, knowing he'd find her there and planning just what he'd do to her with a whole gorram ship at his disposal. He felt frisky as a boy in his first brothel just thinking on it. But then she always had that effect on him. Those big eyes, that wicked smile, the fact she could kill him with her pinkie.

She was waiting just where he'd expected, sitting cross-legged in the middle of the dining table, chewing on a lock of silky dark hair. He grinned at the sight. She looked just like a gorram pixie or some such. He crossed over to her slowly and bent to nuzzle at her neck. She always smelled so great, fruit and cinnamon, like a homemade pie. He breathed deeply and moved his hand to her waist for a squeeze.

"Hey, baby doll," he growled, his lips wandering down over her collarbone and towards the soft upper curve of her breasts. He was enjoying the journey so much, it took him a few seconds to work out she wasn't responding. What the hell? "You know this usually works better when we're both payin' attention," he said.

She looked up at him, looking a little sad. "Feeling strange, unfocused. Not ready to have sex just now."

"Not ready?" he about exploded. "Damn it, girl, you sure do pick your moments. You have any idea how long it's likely to be afore we get the run of the ship again? Without worryin' about gettin' caught every time we so much as touch each other?"

"Don't be angry," she said, sniffling a little and making him feel like some sort of hun dan lowlife. "I didn't choose to feel this way. Emotions are not optional. They drown me."

"Aw hell, I ain't angry. Little frustrated," he admitted, "but I ain't gonna do anythin' you don't want me to." He reached out a hand and tugged at her hair – fascinating stuff, like tangled skeins of silk. "You not feelin' so good?" He ventured this a mite nervously. Wasn't quite sure what he'd do if'n she started talking about her feelings and all.

"Feel strange," she said again, tipping her head on one side. "Head full of fuzz. Feet full of fire."

Huh. Well, that at least he could do something about. He hauled himself up on the edge of the table. "Give 'em here then."

She got that little crinkle above her nose that she always got when he was bemusing her. "I don't understand. What am I to give you?"

"Your feet, damn it. Lie back and stick 'em in my lap."

She looked at him as if he'd lost his wits but did as he said. He took one slender white foot in his hands and started rubbing. Hell, it was kind of nice touching her like this, he thought, as he moved his thumb in circles around her instep. He was so engrossed in what he was doing he didn't see his girl's face as she watched him.

* * * * * * * *

Just when she thought the man that was Jayne Cobb could offer no more surprises, he did. She took in the concentration on his face and realised it was the same expression he wore when he cleaned and polished his beloved weapons. It made her feel cherished. Gave her hope that this was more than just an animal attraction, two wild creatures mating.

Her hand moved down over her stomach and she felt the faintest flutter inside, like the beating of a butterfly's wings. Her lips tilted in an enigmatic smile and she sighed happily. Perhaps it would be all right after all.


	2. Cause and Effect

**Cause and Effect**

It was a conundrum. River had spent the past week analysing possible permutations and connotations, trying to deduce the method with the best outcomes. But whichever way she calculated it, Jayne was going to get a shock.

He would probably shout and rave a bit at first, since that was his habitual response to matters of stress. Then he would sulk, and work his way through blaming her (because he could), Simon (because he always did) and everyone else (because they were there). She knew he would come round to the idea in the end and even feel guilty about lashing out, and truly she didn't blame him for his reactions. She knew they rose from a deep-seated insecurity and a dislike of change of any sort. Jayne was a mountain, strong and rooted – the elements might wear away bits of the surface, but at his core he remained unchanged.

Still, he was going to be deeply unpleasant to live with in the meantime. And that wasn't even taking into account that, in his alarm at her news, he was likely to let slip to the rest of the crew exactly how the situation had arisen. River wasn't sure if any of them suspected that her relationship with the sullen mercenary had undergone a shift. She thought that Inara looked at her oddly now and then. That could be for some other reason, of course, but if anyone on board could detect connections between hearts it would be the companion.

At times, River ached to pour out her feelings to someone like Inara, or perhaps Kaylee, another girl to giggle and sigh with over her first romance. But Jayne had thought they should keep it to themselves and she had agreed with his logic. At the time, it had been a casual thing, scratching an itch with a convenient body, so not telling the others had seemed the best course of action. They wouldn't understand such a relationship. Then, over a month or so, it had developed into something more, something elusively sweet and wondrous. And now it would change again, ever evolving, ripples of alteration spreading out into every aspect of their lives.

She had to tell him.

It took some time to set up the cargo bay as she wanted it. Everything had to be placed with precision, coordinated and triangulated, angles and dimensions perfectly aligned. Getting Jayne to go down there with her proved even more challenging.

"Why we gotta go there?" he asked suspiciously, shovelling a bowl of rice and pork into his mouth. The man never stopped eating.

"Because I have something to show you," she said patiently.

He perked up at that. "Wouldn't my bunk be better for that, darlin'?"

"Not that," she said, rolling her eyes. "Something else."

"What else is there?"

"That sort of attitude is exactly what got us into this predicament in the first place," she pointed out.

"Pre-what-a-mint?"

River sighed. "Just come to the cargo bay, Jayne. Things you must know. Have to show you the big picture."

"We ain't transportin' no art, are we?" She took the bowl out of his hands and dragged him out of his chair in the end, although he grumbled all the while. But he bent down and pressed a hot, open-mouthed kiss on her shoulder in the corridor when he was certain no one else was around. She hummed with pleasure, nerve ends tingling at the contact.

When they got to the cargo bay, he looked perplexed. "What the hell is all this junk?"

"An experiment," she said, flashing him a smile and skipping off to the top of the catwalk. "Stand on the treasure spot."

He did as she told him, moving down into the centre of the cargo bay and standing on the large X she had made there with yellow tape. Bouncing on her toes with excitement, River plucked the large ball bearing out of her pocket and positioned it before releasing it into the system. It slid down the metal chute, gaining speed all the while, before dropping down to trigger the spiral and the switch. The reaction sped off in both directions, metal and plastic swinging back and forth in rhythmic potentiality. She watched the pieces dance according to her directions, rattling and bouncing, zig-zagging and falling. Finally, the last pieces of the puzzle snapped into place, showering Jayne simultaneously with a bag full of coins and a bucket of cold water.

His howl of reaction made River bite her lip and scamper down the steps to the cargo bay floor. A confused, wet and angry Jayne glared at her. "What the hell was that for?"

"Demonstration," said River nervously, reaching out for his hand. "Cause and effect."

"Well, near as I can see it, the effect is me gettin' bruised and soaked, and the cause? IS YOU!" he roared.

"Ball bearing in actuality," River clarified, "although one could argue that I instigated the initial movement and so it wasn't actually a contained system."

Jayne just stared at her, dripping quietly. "Huh?"

"Wanted to show how one small alteration can have wide-ranging effects. Trying to tell you something, but not sure how to show all the repercussions, both positive and negative."

Jayne shook his head like a dog, water spraying everywhere. He started to wring out his T-shirt and River got the uncomfortable impression that he was pretending it was her neck. She gulped.

"So what exactly were you tryin' to tell me with this little demonstration a'yours? That you've gone all crazified again?"

River shook her head. "Trying to tell you that one of your swimmers got through the net."

"Come again?"

"That may well have contributed to the problem, yes."

Jayne ran his fingers through his short dark hair in exasperation. "Look, girl, at least one of us ain't understandin' head nor tail a' this conversation."

"One and one are soon to make three," she said, not sure how to make it any more obvious. "DNA has merged, new life created."

"Woah," Jayne said, eyes widening in dawning realisation. "You sayin' what I think you're sayin'? You and me gonna have ourselves a little'un?"

She nodded, unable to look directly at him as she waited for the fireworks to explode.

"Well, how the ruttin' hell did that happen?" he yelled. "Ain't we always been real careful? What the hell use is swimmin' with yer boots on if you end up gettin' bit on the toes anyhow? Coulda skipped the ruttin' condoms if that's all the good they're gonna do!"

"The seed is strong and will strive to lay down roots at any cost," River said.

"You callin' me a weed, girl?"

She giggled and inched closer. He was taking it better than she had anticipated. She stroked her fingers down the back of his hand, wanting to reassure him that it would be all right. He turned his hand and grasped hers, calloused fingers gripping firmly and tugging her towards him.

"You okay with this?" he said quietly. "You ain't scared or nuthin'?"

"Not as long as I have my Jayne."

"Always. You know that, right."

She smiled happily. "Know now."

They jumped apart as a voice broke into their reverie. "Ta ma de! What the hell happened to my cargo bay?"

"Er, River was splainin' cause an' effect to me, Captain. Just a little physical demonstration." Jayne winced at the poor choice of words.

Mal leaned on the catwalk rail and put his head in his hands with a groan. "River?" he said.

"Yes, Captain."

"I know Jayne ain't the sharpest tool in the box," Mal said, "but can you contrive to explain stuff to him in the future without resorting to rearranging all our cargo and spare parts?"

"Won't need to explain anything else," River said, grinning cheekily up at Jayne. "Jayne understands perfectly."

"Well, I'm sure glad somebody round here does…" Mal said, looking at the mismatched pair standing in a puddle in the middle of his cargo bay. "Cause me? I'm all manner of confused."


	3. Making Waves

**Making Waves**

It was Inara who noticed first, as River had thought it might be. The companion was astute in matters of the heart and the flesh, at least as pertained to other people. She had noticed a discordant note in the relationships of the crew for some time but had thought it was just her ongoing situation with Mal that had made her overly sensitive. When she saw Jayne stroke River's hand at dinner one night, it took her a moment to realise what she had witnessed. The girl's hand had crept over towards his plate, probably to snaffle some food while he wasn't paying attention, but instead he reached out to trap it beneath his own then turned it over and rubbed his thumb gently across her palm, never breaking off his conversation with Mal and Zoe.

Inara's eyes widened. It was the lack of conscious thought in the gesture that was most telling. Neither he nor River seemed surprised by his action. In fact, the girl smiled shyly to herself as she nimbly wielded her chopsticks with her free hand.

"River, dear," Inara said softly and then looked pointedly at where their joined hands still lay on the tabletop. River flushed and tugged her hand away quickly, glancing nervously back at Inara and then at the others to see if anyone else had noticed. Inara didn't think they had. They weren't the most observant bunch of people: Kaylee and Simon only had eyes for each other these days, and Mal and Zoe had been deep in conversation with Jayne about the next mission. For herself, Inara decided to keep quiet for now. It wasn't her secret to share, and she didn't know all the details anyway. Perhaps she should have a word with River, though. If something _was _going on between the fey assassin and the socially challenged mercenary – and what a strange thought _that _was – River would undoubtedly need her professional advice.

* * * * * * * *

Zoe still wasn't back to her usual self, she'd be the first to admit that. Even now, several months after Miranda, she felt physical pain when she thought of her husband. Everyone said that grief lessened over time, but it hadn't yet, not for her. So she took a while to pick up on the nuances of behaviour and body language among the crew. Simon and Kaylee were fairly obvious, of course, and Mal and Inara seemed to be tiptoeing around each other even more than usual these days, making her wonder what exactly had happened between the two of them.

What really took her by surprise, though, was the change between Jayne and River. They were both very physical beings, much like herself, and they probably didn't realise just how much they gave away in their stance and movements. At first, she watched with a kind of bemusement – it was a distraction from thinking of herself and all she had lost. Gradually, she realised it wasn't a casual thing. There was something going on there. Something… established. She wondered when it had started. And she wondered why she didn't feel the urge to run and tell Mal.

Perhaps she of all people understood what it was to grab hold of a little happiness. You never knew when it might be snatched away from you.

* * * * * * * *

Going down to the cargo bay to look for a spare part for her beloved engine, Kaylee didn't realise right away what she had stumbled on. When she heard the first moan, her initial thought was that someone had hurt themselves and she almost called out to see if they needed help. Then another, deeper, more guttural groan joined with it and she realised it was the good kinda hurtin'. She stifled a giggle and crept between the boxes, trying to get closer. It had to be Mal and Inara, surely. They'd been acting mighty strange lately, all prickly and polite, something had been bound to snap. And from the sound of all that panting, it was snapping real well.

Then she peeked around the pile of boxes into the corner and saw who was doing all the sexin'. Her mouth fell open as she took in the site of River spread-eagled on a crate, with her skirts all mussed up round her waist and Jayne's head buried between her thighs. As Kaylee stood there in shock, River grasped his hair and tugged.

"Inside. Now," she demanded in breathy tones. A leer crossed Jayne's face.

"Anything for my girl," he growled and started crawling his way up her body in a way that made Kaylee break out in a hot flush. She turned away quickly and shut her eyes.

'Wow,' she thought when she was capable of thinking straight. 'When did this happen?' She thought briefly about whether to bring this up with Simon, or the Captain, and decided against it. It had all looked pretty gosh-darn consensual to her. And she figured that made it none of their never mind.

Serenity might have to wait a while to get serviced, though, at least until her crew had finished servicing each other…

* * * * * * * *

Simon didn't put two and two together right away, but then he can be a bit of a boob sometimes, as his sister is fond of remarking. When she started throwing up in the mornings he thought it was a bad reaction to her medication (not that she took much any more) or perhaps something wrong with the food or water supplies. After testing everything on board, much to Mal's chagrin, he couldn't find any possible source of the illness. Then she keeled over one day in the infirmary and he managed to draw a sample of blood before she woke up again. She insisted she was fine, of course, and kissed him on the cheek with a smile telling him not to worry.

Of course, worrying was what he did best. He tested that blood every which way to Sunday and found that she was frighteningly healthy – as close to a perfect physical specimen as he could find. He was frustrated. That was the only reason he did the hormone analyses at all, sheer desperation. Desperation that was nothing compared to what he felt when the results came up.

Pregnant.

How in the name of all that was holy had she gotten herself pregnant?

They'd only set down at a couple of worlds in the last few months, still trying to keep a low profile, and she'd barely had time to get up to anything on those occasions. Still, someone had impregnated his baby sister, all right. He didn't know how to break it to her. How she would take it. This was a disaster.

He watched her closely over the next few days, until Mal asked if he needed glasses with all that squinting. He couldn't find any trace that she might be worried or nervous, so could only conclude that she wasn't aware of the baby yet.

That is until he saw Jayne brush the back of his hand surreptitiously against her still-flat belly. He just stared at it for a moment and then looked up just in time to see his baby sister, innocent little River, give that big lug what could only be described as a come-hither look. His jaw dropped.

"You aimin' to catch some flies?" Mal said. "What in tarnation's wrong with you today, Doc? Kaylee not been lettin' you get enough sleep?"

Kaylee grabbed his arm at that point and hoisted him from the table. "Don't think he's feelin' too good, Cap'n. He's lookin' a mite peculiar." And with that, she dragged him from the room all the way to her bunk.

He was still gibbering. "But she…? And he…? And they…? Oh, god."

"Jayne and River, right?" Kaylee said with a wry smile.

He turned to her in shock. "You knew?! And you didn't tell me?!"

"Didn't think it was any of our business. You don't see either of them interferin' in our relationship, do ya? 'Sides, I've only known for a few days. Walked in on 'em sharin' a private moment, if ya know what I mean," she said with a wink.

Simon shuddered. "Kaylee, the furnishings know what you mean. I just… I can't believe she'd keep this a secret from me."

"Might not have thought you'd understand. Might have thought you'd freak out a l'il bit. Can't imagine where she'd get such an idea…"

"I might not understand, but she's my sister. I just want her to be happy."

"Well, darlin'," Kaylee said, putting her arm around him as he dropped his head onto her shoulder. "If it's any consolation, she looked _real_ happy when I saw her."

"Eww, I don't want to have to think about my little sister that way, thank you very much. Bad enough I have to be the one to deliver the baby, since I doubt anyone else on board is going to volunteer."

"Baby?!" Kaylee shrieked, right in his ear. He tried desperately to shush her. "They're gonna have a baby? That's so shiny! They'll just be the cutest li'l family."

"The thought fills me with terror," Simon said drily. "Perhaps I should take out shares in some armament manufacturers."

* * * * * * * *

The whole family group was gathered round the dinner table a couple of nights later, talking and laughing in a way they hadn't done in quite a while. Mal and Inara seemed to have called some sort of truce and were even sitting next to each other without looking uncomfortable. For a while, they'd left an empty chair at the table, no one wanting to admit that Wash wasn't going to be sitting there any more. Now, though, the chairs were evenly distributed, three at each side and Mal at the head of the table. When River put her hand over her mouth at the end of the meal, only Jayne noticed at first.

"You okay?" he said in an undertone.

She nodded, then whispered, "The smell of the coffee is… displeasing to my system. Insides coming out if stimuli is not removed."

"Whoa," he said. "Might put a crimp on dinner. How 'bout I shift the pot over to the counter?"

She smiled up at him in thanks as he grabbed the coffee pot and carried it over to the side of the mess, out of smelling range.

"Uh, Jayne," Mal said. "Some of us weren't finished with our coffee yet. You wanna bring that back over here?"

"Can get up and walk fer it, can't ya? Smell's makin' River feel sick."

"Yes, that's quite a common reaction…" Simon began before biting his tongue and flushing slightly. River and Jayne both stared at him with wide eyes, while Kaylee hid her face in her hands.

"You know?" River whispered.

"Oh, mei-mei," Simon said and reached over to hold her hand. "You could have just told me, you know. I promise I'd only have freaked out a little."

"Then you know…" and her eyes glanced over at Jayne, who looked as though he was nervously gauging where the first attack was going to come from.

Simon sighed. "Unfortunately, yes. I can't pretend to understand your choice, but you're a grown woman and as hard as it is for me to accept that, I don't have any right to dictate how you live your life." He smiled at her ruefully. "You've already missed out on too much of it."

"Mighty generous of you, Doc," Jayne grudgingly acknowledged. "Some guy knocked up my sister, I'd beat him to a bloody pulp."

"Yes, well, your talents do lie more in that direction than do mine. Just one thing, however," he said, fixing Jayne with a cold stare that made even the battle-hardened mercenary feel uneasy. "Break her heart and I'll break your spine."

"Fair 'nough," Jayne said gruffly. "Don't intend on doin' any such thing, but if'n I did, reckon I'd deserve that."

"Well, now, as touching as all this male bonding is," Mal drawled, "would someone do me the courtesy of tellin' me what the ruttin' hell is goin' on around here? 'Cause I've got some nasty suspicions taking root in my brain and I'm really hopin' for the good of my sanity they turn out not to be true."

Everyone looked at each other, nobody wanting to be the one to break the news to the captain. Finally, River spoke up. "The stork has made an appointment. He will be bringing a bundle of joy in one hundred and seventy-eight days, four hours and seven minutes. Not yet decided on name."

"Bundle of…? A baby? Our li'l albatross is havin' a rugrat? Then who the hell's the fa--- Oh no! No, no, no, no, no! Jayne, did we _not _talk about the Special Hell?"

"Hey, I'll have you know _she _seduced _me_! I was an innocent victim. Ow! What'd ya punch me for, ya little hellcat?"

"Not nice to imply unwilling participation. Decision was mutual, and mutual pleasure was had."

"Sure was," Jayne said, with a piratical grin. "Five times, as I remember."

Several pairs of hands slapped over ears in denial. "Gorramit, Jayne. Last thing we need is details. You and you," Mal said, pointing at the guilty pair. "So freaky and wrong I don't even know where to start, so I won't. But you knocked her up, Jayne, so you'll be makin' an honest woman of her soon as we can find a preacher."

"Already planned to," the merc said smugly, leaning back in his chair with his hands behind his head. It took only a small push for River to send him sprawling on the floor. "Now what?" he said angrily.

"It is customary to ask the girl," she said primly. "I was merely assisting you onto your knees, where you should be."

"Aw, hell. You gonna make me ask you all formal-like, front a'everyone?"

River merely stuck her nose in the air and drummed her fingers impatiently on the table. Jayne knew that face. That was her 'not budging an inch' face. Figured he'd better do this and get it over with. After all, she was bound to say yes, right? Wasn't she? What if she didn't want to get shackled to a no-good mercenary just cause he'd got her in the family way? Jayne cleared his throat, trying to get rid of the lump that seemed to have lodged there.

"River," he said, not knowing quite how to say it. "I know I ain't one of them fancy Core dandies you prob'ly figured on marryin' one day, and God knows I ain't never gonna be good enough for ya, but if ya give me a chance I'll do my best to show ya, and the baby, and any more we have 'long the way that, well, I… love ya and all." He hazarded a glance up at her and saw a slight smile on her lips that gave him hope. "Will ya marry me, darlin'?"

River threw her arms around his neck, nearly choking him. "Yes. Love you too. And you are very worthy," she said, for his ears alone. "You are my big damn hero."

He pulled back and grinned at her in relief. "Damn straight!" he said.

* * * * * * * *

A/N: This is the original ending point for this story, and it works as such. I haven't marked it as complete, though, because I may want to add additional stories in this particular reality and will post them here if I do. So, if you'd like to see more, let me know! :)


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